It is a well known medical procedure to inject a patient with fluids via needle or catheter devices. The needle may be connected to a fluid injector by a connector tube which transmits fluid to the needle. The connector tube may also draw fluids from a container such as an IV bag. In such fluid injections detecting the presence of extravasations or infiltrations of nonvascular tissue is necessary. Extravasations or infiltrations are detected by measuring temperature changes which trigger an alarm condition upon detection of a predetermined temperature deviation from normal skin temperature.
Present systems for detecting extravasations are useful in IV drug infusion applications where the flow rate is slow enough such that the fluid is at room temperature when it is injected. The present methods thus assume a significant and relatively constant difference between fluid temperature and limb temperature.
However, with regard to computed tomography ("CT") contrast injection applications, where the flow rates from the fluid injector are in the range of 0.1 to 10 ml/s, the response time for temperature sensing is a significant consideration. A current extravasation detector employs an antenna and radiometer to measure the temperature of the subcutaneous tissue where fluid is injected. An alarm processor uses an algorithm to determine alarm conditions. The algorithm measures the temperature signal periodically and compares it to a fixed threshold level. The extravasation detector system's alarm processor communicates with the fluid injector so the start of the injector and the fluid flow rate are known by the alarm processor. The processor records the temperature signal at the start of the injection. The alarm processor will signal an alarm if the magnitude of deviation from the initial signal exceeds a predetermined magnitude threshold. The magnitude thresholds are taken from tables stored by the processor. The threshold values are predetermined as a function of flow rate and the values are stored in the tables. The alarm signal allows the processor to shut down the fluid injector to prevent further extravasations.
However, additional problems are inherent in temperature sensing in extravasation detection. In CT contrast injections, the fluid is usually, but not always, warmed to a temperature near body temperature. The fluid in the connector tube and the connector tube itself are usually at room temperature. Normally, cold fluid is initially injected, followed by warmer fluid. The cold fluid may cause false positive alarms, as a small amount of cold fluid in a blood vessel can cause a signal change identical to that of a larger amount of warmer extravasated fluid. Furthermore, using preset thresholds does not account for variations in initial patient limb temperature nor variations in fluid temperature during the injection.
Recent passive patient measurement data indicate that limb temperature varies more than had been previously expected. Fluid at 37 degrees Celsius, which is the nominal body temperature, may be warmer than the limbs of most patients. This difference affects the magnitude thresholds for any extravasation decision criteria. Additionally, several patient-specific factors may be useful in setting thresholds to minimize false alarms (false positives) while being sensitive to true extravasations. However, predetermined thresholds cannot take these patient-specific factors into account.
Thus, an extravasation and infiltration detection device is needed which can detect true extravasations in high flow injection situations. Furthermore, a detection device is needed which can detect true extravasations despite patient variation and temperature changes.